Normal (n)-butanol and acetone may be produced by anaerobic fermentation processes as disclosed by Weizmann. Such processes were first commercialized during the period 1914 to 1918. The cultures which were developed and discovered by Weizmann are the anaerobic bacteria Clostridium Acetobutylicum Weizmann. Using feed stock materials such as corn and horse chestnuts, these bacteria produce n-butanol and acetone in commerical yields. During World War I, the process was used primarily for obtaining acetone for the manufacture of explosives.
Over the years, improvements were made in the process. There were developed different Clostridium cultures which produced both better yields and different mixtures of solvents including ethanol and propanol. Different feedstock materials such as corn cobs, blackstrap molasses, beet molasses, and others were also used. Furthermore, there were employed other additives as well as nutrients which speeded up the fermentation reaction. The process was operated on a commercial scale until the middle 1950's when cheap petroleum feed stocks as well as processes for making butanol and the other solvents from petroleum became available and petroleum became the primary source for producing butanol.
These fermentation processes have become of greater interest of late due to the recent sharp increase and apparent long term rise in the price of petroleum, coupled with the stable price of farm product feeds for the fermentation. Fermentation products are of current commerical interest as a potential internal combustion fuel to replace the petroleum based fuels. A problem exists, however, with the Weizmann fermentation process because the maximum concentration of butanol is of the order of 2.5% before the bacteria are inactivated. The distillation recovery methods used to separate these solvents require a tremendous amount of energy.
The search has continued for improved processes and apparati for producing n-butanol on a continuous, economical basis. This invention was made as a result of that search.